diff options
Diffstat (limited to 'Documentation/mn10300/ABI.txt')
| -rw-r--r-- | Documentation/mn10300/ABI.txt | 149 |
1 files changed, 0 insertions, 149 deletions
diff --git a/Documentation/mn10300/ABI.txt b/Documentation/mn10300/ABI.txt deleted file mode 100644 index d3507bad428d..000000000000 --- a/Documentation/mn10300/ABI.txt +++ /dev/null @@ -1,149 +0,0 @@ - ========================= - MN10300 FUNCTION CALL ABI - ========================= - -======= -GENERAL -======= - -The MN10300/AM33 kernel runs in little-endian mode; big-endian mode is not -supported. - -The stack grows downwards, and should always be 32-bit aligned. There are -separate stack pointer registers for userspace and the kernel. - - -================ -ARGUMENT PASSING -================ - -The first two arguments (assuming up to 32-bits per argument) to a function are -passed in the D0 and D1 registers respectively; all other arguments are passed -on the stack. - -If 64-bit arguments are being passed, then they are never split between -registers and the stack. If the first argument is a 64-bit value, it will be -passed in D0:D1. If the first argument is not a 64-bit value, but the second -is, the second will be passed entirely on the stack and D1 will be unused. - -Arguments smaller than 32-bits are not coalesced within a register or a stack -word. For example, two byte-sized arguments will always be passed in separate -registers or word-sized stack slots. - - -================= -CALLING FUNCTIONS -================= - -The caller must allocate twelve bytes on the stack for the callee's use before -it inserts a CALL instruction. The CALL instruction will write into the TOS -word, but won't actually modify the stack pointer; similarly, the RET -instruction reads from the TOS word of the stack, but doesn't move the stack -pointer beyond it. - - - Stack: - | | - | | - |---------------| SP+20 - | 4th Arg | - |---------------| SP+16 - | 3rd Arg | - |---------------| SP+12 - | D1 Save Slot | - |---------------| SP+8 - | D0 Save Slot | - |---------------| SP+4 - | Return Addr | - |---------------| SP - | | - | | - - -The caller must leave space on the stack (hence an allocation of twelve bytes) -in which the callee may store the first two arguments. - - -============ -RETURN VALUE -============ - -The return value is passed in D0 for an integer (or D0:D1 for a 64-bit value), -or A0 for a pointer. - -If the return value is a value larger than 64-bits, or is a structure or an -array, then a hidden first argument will be passed to the callee by the caller: -this will point to a piece of memory large enough to hold the result of the -function. In this case, the callee will return the value in that piece of -memory, and no value will be returned in D0 or A0. - - -=================== -REGISTER CLOBBERING -=================== - -The values in certain registers may be clobbered by the callee, and other -values must be saved: - - Clobber: D0-D1, A0-A1, E0-E3 - Save: D2-D3, A2-A3, E4-E7, SP - -All other non-supervisor-only registers are clobberable (such as MDR, MCRL, -MCRH). - - -================= -SPECIAL REGISTERS -================= - -Certain ordinary registers may carry special usage for the compiler: - - A3: Frame pointer - E2: TLS pointer - - -========== -KERNEL ABI -========== - -The kernel may use a slightly different ABI internally. - - (*) E2 - - If CONFIG_MN10300_CURRENT_IN_E2 is defined, then the current task pointer - will be kept in the E2 register, and that register will be marked - unavailable for the compiler to use as a scratch register. - - Normally the kernel uses something like: - - MOV SP,An - AND 0xFFFFE000,An - MOV (An),Rm // Rm holds current - MOV (yyy,Rm) // Access current->yyy - - To find the address of current; but since this option permits current to - be carried globally in an register, it can use: - - MOV (yyy,E2) // Access current->yyy - - instead. - - -=============== -SYSTEM CALL ABI -=============== - -System calls are called with the following convention: - - REGISTER ENTRY EXIT - =============== ======================= ======================= - D0 Syscall number Return value - A0 1st syscall argument Saved - D1 2nd syscall argument Saved - A3 3rd syscall argument Saved - A2 4th syscall argument Saved - D3 5th syscall argument Saved - D2 6th syscall argument Saved - -All other registers are saved. The layout is a consequence of the way the MOVM -instruction stores registers onto the stack. |
